Dieback and mortality of Nothofagus in Britain: ecology, pathogenicity and sporulation potential of the causal agent Phytophthora pseudosyringae

Abstract

Since 2009 extensive dieback and mortality of Nothofagus obliqua, associated with bleeding cankers on stems and branches, has been observed in the UK. The causal agent was identified as Phytophthora pseudosyringae, based on morphological and analysis of the internal transcribed spacer (ITS) sequences. Between 2011 and 2013, a survey assessed the frequency and nature of these P. pseudosyringae infections. Mature trees of Nothofagus with stem lesions caused by P. pseudosyringae were found across England, Scotland and Wales. Additional symptoms such as twig blight and leaf necrosis indicated that aerial infection was occurring. Besides N. obliqua, other hosts regularly encountered included Nothofagus alpina, Fagus sylvatica and Vaccinium myrtillus. In pathogenicity tests involving inoculation of logs, P. pseudosyringae was shown to be an aggressive bark pathogen of N. obliqua and F. sylvatica, but significantly less aggressive on N. alpina. Foliage susceptibility and sporulation tests showed marked differences between the six host species tested. Leaves of N. obliqua and V. myrtillus were highly susceptible. Leaves of N. alpina were moderately susceptible, those of Rhododendron ponticum slightly susceptible and those of F. sylvatica not susceptible at all. High levels of sporulation were observed only on inoculated N. obliqua and V. myrtillus leaves. This suggests that P. pseudosyringae may sporulate heavily on N. obliqua foliage in the field and that this inoculum initiates the aerial lesions observed on the shoots, branches and stems. The results also suggest that P. pseudosyringae has the potential to pose a serious threat to N. obliqua and other Nothofagus species in their Southern Hemisphere native ranges.

Multiple new cryptic pathogenic Phytophthora species from Fagaceae forests in Austria, Italy and Portugal

“…This is similar to that of other possibly endemic low-temperature Phytophthora species such as P. ilicis , P. pseudosyringae , P. psychrophila, and P. quercina (Jung et al 1999, 2002, Pérez-Sierra et al 2013, Scanu et al 2014b, Scanu & Webber 2016). All four new species are homothallic, with a high oospore wall index (range 0.4–0.5) enabling them to survive both the long hot and dry summers typical of Mediterranean regions ( P. castanetorum , P. tyrrhenica, and P. vulcanica ) and cold winters in Austria ( P. tubulina ), on Mount Etna ( P. vulcanica ), and in the Gennargentu Mountain and Serra da Estrela ( P. castanetorum ).…”

Phytophthora pseudosyringae associated with the mortality of Nothofagus obliqua in a pure stand in central‐southern Chile

“…Tissue samples obtained from the margin of necrotic lesions were disinfested for 30 s in 70% ethanol and washed three times in sterile distilled water (SDW) (Scanu & Webber, 2015). Samples were blotted dry and plated onto PAR-CMA selective medium (piramicin 10 mg −1 , ampicillin 250 mg −1 , rifampicin 10 mg −1 , CMA 17 g −1 L) and incubated at 20°C for 3-4 day in the dark.…”

“…Twigs of 20-30 cm in length, 2-3 cm diam., were inoculated with P. pseudosyringae isolate A2 (from a canker) mycelium discs (3 mm) (Scanu & Webber, 2015). Twigs of 20-30 cm in length, 2-3 cm diam., were inoculated with P. pseudosyringae isolate A2 (from a canker) mycelium discs (3 mm) (Scanu & Webber, 2015).…”

Multispecies Phytophthora disease patterns in declining beech stands

“…However, sparse production of caducous sporangia has been reported for certain species and may occur more frequently in a natural environment (Scanu & Webber, 2016). Water splashing combined with human activities and game animals, as well the presence of livestock, could also explain dispersal of predominantly soil-borne Phytophthora species outside the soil environment (Scott, Burgess, & Hardy, 2013).…”

“…Infection eventually progresses into the cambium and xylem, and plants develop collar rot and bleeding lesions on stems, signifying areas of infected and necrotic tissue in the underlying bark (Davison, Stukely, Crane, & Tay, 1994;Giesbrecht, Hansen, & Mitin, 2011). This ability has largely been attributed to the production of caducous sporangia favouring aerial dispersal (Erwin & Ribeiro, 1996;Scanu & Webber, 2016 This ability has largely been attributed to the production of caducous sporangia favouring aerial dispersal (Erwin & Ribeiro, 1996;Scanu & Webber, 2016 …”